Prior to the onset of labor, a pregnant patient prefers to be ambulatory. In other words, the pregnant patient prefers to be able to move about freely, whether in the patient's own home, or within the hospital. However, a pregnant patient whom is likely to begin labor soon, has reduced ambulatory ability due to the number of sensors that are normally attached to their abdomen to monitor both the onset of labor as well as the health of the unborn baby.
The two most common transducers attached to the pregnant patient are transducers to monitor the fetal heart rate (FHR) and transducers to detect uterine activity (i.e. contraction). The fetal heart rate is typically monitored by a non-invasive system using a doppler ultrasound technique to detect the motion of the beating heart of the fetus. The beating heart of the fetus produces a doppler shift in the ultrasound signal received by the transducer. The doppler shift frequency is then translated into the fetal heart rate. The uterine activity of the pregnant patient is monitored using a separate device known as a tocodynamometer. The tocodynamometer uses pressure or displacement to detect uterine contractions. In one embodiment of a tocodynamometer, a pressure transducer, such as a depressible button, is affixed to the abdomen of the pregnant patient such that the pressure of the abdomen may be detected, and contractions monitored. Alternatively, the tocodynamometer may utilize a strain gauge disposed between one or more points affixed to locations on the patient's abdomen, such that the expansion and contraction of the patient's abdomen may be detected. The tocodynamometer uses the measured pressure, displacement, or strain to determine the relative strength of the contractions.
The FHR monitor and the tocodynamometer are typically held into place in a communicative relationship with the abdomen of the pregnant patient by large elastic bands that are placed around the abdomen of the patient. The elastic bands may also hold a battery pack and a transmitter, such that the FHR monitor or the tocodynamometer may be powered at a remote location, and the detected signals may be sent back to a base transmitter for recording and monitoring the FHR and uterine activity. While this system allows for the pregnant patient to be ambulatory to some extent prior to labor, typically a separate FHR monitor is needed for each fetus of the pregnancy. Therefore, a patient with a multiple fetus pregnancy may be required to have one FHR monitor attached to her abdomen per fetus of the pregnancy in addition to the tocodynamometer measuring her uterine activity. Each additional separate transducer system adds to the weight that the pregnant patient must carry around when ambulating. Furthermore, the individual monitoring devices are relatively heavy, especially the tocodynamometer. The power requirement of each of these transducers necessitates relatively larger battery packs to power the transducers which further adds additional weight. This additional weight makes the task of moving even more difficult to the pregnant patient beyond the difficulty of moving associated with the pregnancy.
Alternative embodiments comprise a combination ultrasound FHR monitor and a tocodynamometer. However, these devices suffer from the combination because the resulting combination produces a substantial weight to be held in one position on the patient's abdomen. Furthermore, the combinational systems require separate control and monitoring circuitry. This requires additional battery capacity, resulting in even more weight attached to the patient. The combination devices limit the pregnant patient's ambulation prior to labor.
Therefore, it is desirable in the field of non-invasive patient monitoring to provide a combinational fetal heart rate monitor and uterine activity monitor. It is further desirable in the field of non-invasive patient monitoring to provide a uterine activity monitor with reduced weight and power consumption needs.